Fuel injection apparatus for internal combustion engines of the liquid-fuelinjection compression-ignition type

ABSTRACT

A fuel injection system for an internal combustion engine of the liquid-fuel-injection compression-ignition type, having a fuel pump arranged to deliver fuel under supply pressure via a pressure-reducing valve to a pressure chamber of an injection plug, the said plug having an injection valve arranged to open in response to the pressure in the pressure chamber and controlling the injection of fuel from the chamber through the nozzle into the associated combustion chamber. The pressure-reducing valve is of the spring-loaded-piston variable-orifice type and when operative controls the fuel pressure in the pressure chamber, and hence the injection pressure, to a predetermined reduced value for the purpose of reducing engine noise during periods of idling. Means is provided however for rendering the pressurereducing valve inoperative when full injection pressure is required, either by bypassing the pressure-reducing valve altogether so that the fuel pump delivery passes directly to the pressure chamber throughout the whole of each pump delivery stroke, or by bypassing the restricted orifice of the pressurereducing valve during the final stage only of each delivery stroke of the fuel pump. In either case the bypassing means may be operated by a running control member of the engine, for example a fuel or speed control member.

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[72] Inventors Wlillam M. Scott 3,456,884 7/1969 Knight et a1. 239/533 iw lvllllll t N rth L 1 FOREIGN PATENTS r an mg on, ant: lng; RoyumnGordon ewe, pp g, 8 6513359 4/1966 Netherlands 239/533 01 EnglandPrimary Examiner-M. Henson Wood, Jr. [21 App]. No. 864,123 AssistantExaminer-Edwin D. Grant [22] Filed Oct. 6, 1969 Atlurney-Watson, Cole,Grindle & Watson [45] Patented Dec. 114, 1971 [73] Assignee Ricardo &Cm, lEngineers(l927) Limited shommmmrswySussexlEmzhand ABSTRACT: A fuelin ection system for an internal combustion engine of theliquid-fuel-injection compression-ignition type, having a fuel pumparranged to deliver fuel under supply pressure via a pressure-reducingvalve to a pressure I54] FUEL INJECTIUN APPARATUS FOR INTERNAL chamberof an injection plug. the said plug having an injection COMBUSTIONENGINES OF THE LHQUlmFUEL valve arranged to open in response to thepressure in the pres- ]NJEUHON (:OMPRESSHONJGNWHON TYPE sure chamber andcontrolling the injection of fuel from the Hanna, Drawing mt chamberthrough the nozzle into the associated combustion chamber. Thepressure-reducing valve is of the spring-loaded- [52] 11.3. CI 239/533,piston variableoritice type and when operative Controls h I 123/32 137/fuel pressure in the pressure chamber, and hence the injection [51]lint. C11 1805b 1/30 pressure to a predetermined reduced value f hPurpose f [50] FllEld 011 Search 239/533; reducing engine noise duringperiods f idling Means is 123/32 G; 137/] 10 vided however for renderingthe pressure-reducing valve in- Reicmnces Cited operat ve when full inection pressure '15 required, either by bypassing the pressure-reducingvalve altogether so that the UNITED STATES PATENTS fuel pump deliverypasses directly to the pressure chamber 2,173,814 9/1939 Bischof.....239/533X throughout the whole of each pump delivery stroke, or by2,813,752 1 1/1957 Pringham 123/32 G bypassing the restricted orifice ofthe pressure-reducing valve 3,104,817 9/1963 Vander Zee et a1. 239/533 Xduring the final stage only of each delivery stroke of the fuel3,348,488 10/1967 Wolff 123/32 G pump. In either case the bypassingmeans may be operated by 3,387,597 6/1968 Wirsching 123/32 G a runningcontrol member of the engine for example a fuel or 3394,891 7/1968 Voit239/533 speed control member.

/ i g a v if 755 18B 78 /-24 74A 76B k, v I t 7L u f K N t Annd v, '462/ 3] L 20 33 22 21 36 19 27 78A 32 23 II I 7 9 States te MENTEU HEB 1 A19?"! SHEET 5 OF 5 fidw p /waif ATTORNEY This invention relates to fuelinjection apparatus for internal combustion engines of theliquid-fuel-injection compressionignition type, of the hind comprisingfuel delivery means, in the form of a reciprocating fuel pump or otherfuel metering and delivery means, arranged to deliver fuel underpressure in predetermined quantities during delivery periods atappropriately timed intervals to at least one fuel injection device ofthe type which includes a nozzle and a valve (herein called theinjection valve) controlling the flow of fuel through the nozzle and soarranged as to be opened automatically during each delivery period bythe fuel pressure in a pressure chamber in the injection device, usuallyadjacent to the injection orifice or orifices, to which chamber the fueldelivery means delivers the fuel. Such fuel injection apparatus isreferred to herein as being of the kind specified.

The injection apparatus to which the invention is applied may be of theusual type employing as the fuel delivery means a reciprocating fuelpump incorporating control means by which the quantity of fuel deliveredduring each injection period is controlled by varying the length of theeffective part of the pump delivery stroke, although the invention mayalso be applied to fuel injection apparatus of the kind specifiedemploying other forms of fuel delivery means in which a measuredquantity of fuel is delivered to the injection device dur ing eachinjection period.

One of the disadvantages of reciprocating internal combustion engines ofthe liquid-fuel-injection compression-ignition type (and particularlythose of relatively small capacity as are used in road vehicles) ascompared with engines of the vaporized charge spark ignition type, isthat they tend to be noisy, particularly when idling and at low speeds.

Research into the cause of the noisy operation has shown that asubstantial proportion of the noise, including the well known dieselknock," appears to result from the high rate of injection inherent inexisting injection systems, augmented in some cases by the fact that, atthe delivery pressures employed, there is appreciable volumetricelasticity in the part of the system between the pump and the injectiondevice which tends to delay the injection while pressure builds up inthis part of the system until the injection valve opens, whereuponinjection begins at a high volumetric rate. Moreover in existing systemsthere is a substantial delay between the beginning of injection and theinitiation of burning, and the result, which is attributed to one orboth of these causes, is that when burning begins, there is a rapidinitial pressure rise in the engine cylinder and consequent noisyoperation. It has also been found that if the rate of the initialpressure rise can be reduced, as by reducing the initial rate ofinjection and/or the delay between the beginning ofinjection and thebeginning of burning, the noise is similarly reduced, and variousproposals have, therefore, been made which aim at reducing the rapidityof the initial pressure rise. One such proposal is the injection intothe air charge prior to the main injection (e.g. during the induction orcompression period) of a small quantity of fuel which is insufficient initself to cause an appreciable pressure rise but which ignites beforethe main injection begins so that burning of the fuel then injectedtends to start with little delay. This proposal, which is usually calledpilot injection, has not however, been entirely successful in itspurpose.

it has been found, for example, that at the injection pressures requiredin practice it is difficult to provide for such pilot injection inadvance of the main injection, whether there is a time interval betweenthe pilot injection and the main injection or not, due to the volumetricelasticity referred to which causes the fuel line between the pump andthe pressure chamber of the injector to act to some extent as ahydraulic accumulator so that when the injection valve opens the initialrate of injection is too high for quiet engine operation.

Vnrious other proposals huve also been made for the purpose ofrcducingnoise. including those incorporated in the in jection system forming thesubjects of the present applicants British Pat. Applications Ser. No.43,576 of 1964 and 12,747 of 1965 and f at. l lo. l,0l4,l3l and thepresent invention has for its object to provide forms of fuel injectionapparatus of the general kind referred to which will represent a stillfurther improvement over existing systems.

According to the present invention, in fuel injection apparatus of thekind specified, there is included between the fuel delivery means andthe pressure chamber a pressurereducing valve as defined hereinafterwhich when operative acts in each delivery period to reduce the pressureat which fuel is delivered to the pressure chamber to a determinedconstant reduced value substantially below the full supply pres sure atwhich the fuel delivery means supplies fuel to the pres sure-reducingvalve, and there is also included means for rendering thepressure-reducing valve inoperative during periods when the delivery offuel to the pressure chamber at substantially the full supply pressureis: required.

The term a pressure-reducing valve" as used herein is defined as a valvearranged to regulate a flow of fluid to a con stant output pressure lessthan the pressure at which the fluid is supplied to the valve, the valvehaving a variable orifice through which the fluid flows and whosecross-sectional area is controlled by and in accordance with the fluidpressure downstream of the said orifice in such a manner as to regulatethe said downstream pressure to a constant value despite variations inthe supply pressure. For example, the pressure downstream of the orificemay act on a piston against a stressed spring or other predeterminedload, the resultant movement of the piston being used to vary the valveorifice area.

Preferably there is also included in the apparatus a restricted passage(hereinafter called for convenience a restrictor) arranged in serieswith the pressure-reducing valve and serving when the pressure-reducingvalve is operative to control the rate at which fuel at thepredetermined reduced pressure is delivered to the pressure chamber,this rate being determined by the rate at which fuel at the reducedpressure can flow through the restrictor.

in one type of arrangement according to the invention the said means forrendering the pressure-reducing valve inoperative is arranged tomaintain the pressure-reducing valve opcrative during a predeterminedinitial part of each delivery period and to bypass the pressure-reducingvalve during the remainder of that delivery period.

Thus there may be provided a piston valve device interposed between thepressure reducing valve and the pressure chamber, the piston valvedevice having a pressure face on which the output pressure of thepressure reducing valve acts to move it against a biasing force, andalso having a working face which serves during the initial part of thetotal range of such movement to deliver fuel at the said constantreduced pressure to the pressure chamber of the injection device, and onfurther movement of the piston valve device serves to open a bypasspassage which bypasses the pressure-reducing valve to permit the flow offuel to the pressure chamber at substan tially the full supply pressure.in such an arrangement the restrictor is preferably interposed betweenthe pressure chamber and the said working face of the piston valvedevice which applies pressure to the fuel to be delivered at reducedpressure to the pressure chamber, but the restrictor may alternativelybe disposed between the pressure-reducing valve and the said pressureface of the piston valve device.

Three constructions according to the invention are shown by way ofexample in the accompanying; drawings, in which:

FllG. l is a diagrammatic view of a fuel injection system including afuel pump, a fuel injection device, and one form of pressure-reducingvalve assembly providing one form of fuel injection system according tothe invention;

FIG. 2. is a cross section on an enlarged scale of the fuel injectiondevice and pressurereducing valve assembly incorpornted in the systemshown in FIG. ll;

FIG. 3 is a similar view to FIG. 2 showing an alternative form ofapparatus which may be employed in conjunction with a fuel injectiondevice and a fuel pump as shown in FIGS. 1 and 2 and with appropriatecontrol apparatus to provide an alternative form of fuel injectionsystem according to the invention;

FIG. 4 shows diagrammatically the manner in which the form of apparatusshown in FIG. 3 may be employed in con-' junction with fuel controlapparatus embodying a speedresponsive governor; and

FIG. 4 shows diagrammatically the manner in which the form of apparatusshown in F l6. 3 may be employed in conjunction with fuel controlapparatus embodying a speedresponsive governor; and

FIG. 5 is a diagrammatic view of a further form of apparatus which maybe employed as part of the apparatus shown in FIG. 1 and embodying analternative position for the metering orifice.

t The fuel injection system shown in FIG. 1 comprises the usual fuelpump 1 arranged to deliver fuel in measured quantities at appropriatetimed intervals to the combustion chambers of an internal combustionengine of the liquid-fuel-injection compression-ignition type, which isassumed to be a fourcylinder engine, the quantity of fuel deliveredduring each delivery period being controlled in conventional manner by apump control member 1A actuated by control mechanism 18. For simplicity,since the fuel injection apparatus associated with each of the cylinderswould be the same, the fuel injection apparatus associated with onecylinder only is fully shown and will hereinafter be described. Theapparatus comprises a fuel delivery passage 2 to which the appropriatepump piston delivers fuel in measured quantities in well-known manner,an assembly including a pressure-reducing valve shown generally at 3 towhich the fuel delivery passage 2 is attached, and a fuel injectiondevice generally indicated at 4 of conventional type to which thepressure-reducing valve assembly is attached.

The injection device and the associated pressure-reducing valve assemblyproviding a fuel injection system according to the invention is shown incross section and will now be described with reference to FIG. 2. Thefuel injection device comprises the usual casing 5 provided with a fuelinlet connection 6 to which the fuel delivery pipe from the pump wouldbe directly coupled in a conventional system, but which in H6. 2 isconnected in a manner more fully described hereinafter to the outlet endof the body part of the pressure-reducing valve assembly shown generallyat 3 in FIG. 1. The inlet connection 6 communicates by way of a deliverypassage 7, an annular chamber 8 formed by an annular recess in the upperend of a nozzle member 9, and a further delivery passage 10 in thenozzle member with a pressure chamber 11 from which opens an injectionorifice which is normally closed by an injection valve 12. The valve 12includes a part 13 forming a close sliding fit with a bore in the nozzlemember 9 and an upper part 14 which is acted upon by the lower end of apush rod 15 the upper end of which is acted upon through a thrust member15A by a compression spring 16 whereby the valve 12 is urgedcontinuously towards its seating in the injection orifice. Theconstruction and operation of the injection device above brieflydescribed is of well-known conventional type providing for the liftingof the valve 12 by the pressure of fuel delivered to the pressurechamber 11 and acting on the lower end of the part 13 so that theejection of the fuel from this chamber takes place through the injectionorifice under a degree of control by the valve 12. In the constructionshown in FIG. 2, the pres sure-reducing valve assembly 3 is interposedbetween the delivery passage 2 and the inlet connection 6 of theinjection device and comprises a body part 14A partly housed within andprojecting from a two-part casing 15B, 16B of which the part 158 isprovided with a connection 17 containing the end portion of the fueldelivery passage 2 communicates with an annular chamber 18 formedbetween the bore of the part 158 of the casing and the circumferentialsurface of the body part 14A.

The projecting end of the body part 14A is provided with a flange 18Aand with a screw threaded part 188 which is screwed into the fuel inletconnection 6 of the fuel injection device.

The body part 14A contains a pressure-reducing valve and other parts bywhich the delivery of fuel from the fuel injection pump 1 to thepressure chamber 11 of the fuel injection device is regulated to apredetermined constant reduced value, as follows:

Formed in the body part 14A is a bore having a small diameter part 19constituting a cylinder and a large diameter internally screw-threadedpart 20 the open end of which opens into the fuel inlet connection 6 ofthe injection device. Communicating with the cylinder 19 are two fuelinlet ports 21, 22 both leading from a passage 23 which is in opencommunication with the annular chamber 18, while two parts 24, 25 openout of the cylinder 19. The ports 24, 25 communicate with a commonpassage 26 extending parallel to the cylinder 19 and communicating withthe end of the bore 20 and hence with the fuel inlet passage 6 of theinjection device.

Arranged to reciprocate within the cylinder 19 is a pressurereducingvalve 27 one end of which extends from the bore and is formed with ahead 28 acted upon by one end of a compression spring 29 the other endof which acts on an abutment 30 resting against the end of the part 16Bof the casing 4 formed integral with a guide 31 extending within thespring 29. Also arranged in the cylinder 19 is a piston valve member 32acted upon by one end of a spring 33 the other end of which acts on ametering member 34 screwed into the bore 20 and having formed therein arestricted metering orifice 35, the spring 33 thus serving to urge thepiston valve member 32 always towards the pressure-reducing valve 27 sothat the parts normally occupy the position shown in FIG. 2.

Formed in the reducing valve 27 is a passage 36 which communicates withan annular recess in the circumferential wall of the reducing valve,which recess in turn communicates with the ports 21 and 24. Thearrangement is thus such that when fuel under pressure is initiallydelivered by the fuel pump the fuel pressure is transmitted through thepassage 23, port 21 and passage 36 so as to move the pressure reducingvalve 27 towards the right in H6. 2 against the action of its spring 29.Such movement reduces the effective cross section of the variableorifice constituted by the overlap between the port 21 and the annularrecess 24 in the valve member 27, thereby reducing the fluid pressure inthe passage 36 until it reaches a value which exactly balances the forceof the spring 29. The pressure-reducing valve thus regulates thepressure in the passage 36 to this predetermined constant balancingvalue, determined by the setting of the spring 29, despite variation inthe fuel pressure applied by the pump to the passage 23 and port 21.This movement of the pressure reducing valve into its operative"position closes the port 24 so that the reduced fuel pressure now actsto move the piston valve device 32 to the left in FIG. 2 against theaction of its spring 33, so that it acts as a piston to deliver fuel,which was previously drawn into the chamber containing the spring 33during the preceding injection cycle, through the restricted passage 35to the fuel delivery passage 7 of the injection device and hence to thepressure chamber 11, at a pressure determined by the pressure reducingvalve 27 and at a rate which is jointly a function of this pressure andthe effective cross-sectional area of the restriction 35. It will beseen that when the piston valve device 32 reaches a certain point in itsmovement it brings the ports 22 and 25 into communication so thatthereafter fuel can be delivered at full pressure and at a volumetricrate determined solely by the pump delivery rate via the passages 26 and7 to the pressure chamber 11 ofthe fuel injection device.

In operation, therefore, during each fuel delivery period there isdelivered to the pressure chamber 11 of the fuel injection device firsta quantity of fuel at a reduced pressure determined by thepressure-reducing valve 27 and at a rate which is controlled to a degreeby the cross-sectional area of the restricted passage 35, after whichfuel at full delivery pressure and without any substantial restrictionwill be delivered to the pressure chamber 11 ofthe fuel injectiondevice.

memes At the end of each injection period the pressure-reducing valve 27returns to the positions shown in H6. 1?. under the action of its spring29 and port 2 3 is thus opened to act as a relief passage permitting thepiston valve member 32 to move towards the right in FIG. 2 under theforce of its spring 33 and to displace fluid into the passage M andthrough the orifice 3b into the chamber containing the spring 33, thusallowing the piston 32 to return to the position shown in readiness forthe next injection.

In the arrangement shown in FIG. 3 the pump delivers fuel to the passage37 to which the passage 2 in FIG. I may thus be assumed to be connectedand the pressure-reducing valve assembly comprises a body part 38similar to but shorter than the body part M in FIG. 2 and having a borecomprising a cylindrical part in which lies pressure-reducing valve 3%,and an internally screwthreaded part into which is screwed a meteringmember d containing a restricted orifice it. The passage 37 communicateswith a port d2 similar to the port ml in FIG. 2 while a passage l3similar to the passage 2h leads from a port at in the cylinder in whichthe pressure-reducing valve 39 operates into the delivery passage 7 ofthe injection device. A spring dd corresponding to the spring 29 in FIG.2 acts on the pressure-reducing valve 3'9.

In the arrangement shown in FIG. 3 the pressure-reducing valve 3% inaddition to being axially movable to perform its main function isarranged to be rotatable through an angle of about 90 by means of anactuating member do which permits the necessary axial movement of thepressure-reducing valve 39 against the action ofits spring 45 but has asliding dog-type connection 47 with the thrust member dd through whichthe spring 45 acts so that the actuating member M can impart therequired approximately 90 rotational movement to the valve 39. Thepressure-reducing valve 39 has the usual annulus d9 which normallycommunicates with the passage 42, this annu lus communicating throughtwo diametrically opposite slots 50 in the valve with the inlet end ofthe restriction dll and, in one rotational position of the valve, asshown in FIG. 3, being out of communication with the port Aid. In thisrotational position of the valve 39 therefore all the fuel delivered iscaused to pass through the restriction 4l1l to which it flows at areduced pressure determined by the pressure-reducing valve. By rotatingthe valve 39 through 90, however by means of the control member t6 theslots 50 are brought into register respectively with the passage t2 andthe port dd, thus rendering the pressure-reducing valve inoperative andpermitting fuel to flow freely from the passage 37 through the passagedill, slots M annulus W and passage 33 to the passage ti at full pumpdelivery pressure.

The control member as in this construction may be connected eitherdirectly to the fuel control mechanism 11B of the fuel pump, indicatedin FIG. l, or by appropriate mechanism to a manually orfoot-operatedcontrol member, as shown in FIG. 4i. In FIG. 4! the fuelcontrol member M of the fuel pump 52 is actuated by a speed-responsivegovernor d3 of conventional form the setting of the spring MA of whichis under the control of foot-opcrated mechanism comprising anaccelerator" pedal 54 connected by a link 55 to a lever t'iti one end ofwhich acts on the movable abutment 57 of the spring 533A while duringthe last part of its travel towards the idling" position it acts on alever 53 to move it from the position indicated by the chain line 59into the position shown The lever b is connected by a link 6111), abellcranlt lever er and a link 62 to a lever 63 secured to the controlmember as, and the arrangement is such that movement of the lever 58from the position indicated by the chain line 59 into the posi' tionshown rocks the member 46 through an angle of approximately 90 from theposition in which the pressure-reducing valve 39 is in the position inwhich the slots 5% register with the passage 42 and the port 44 into theposition shown in FIG. 3. Thus, during the range of settings of thegovernor spring 53A corresponding to operation of the engineincorporating the fuel system at appreciable power and/or speed, fuel isdelivered to the injection device substantially without restriction andsubstantially at full delivery pressure throughout the whole of eachdelivery period, through the passage d2, the lots 5ft, the annulus W.the passage ed and the delivery passage 7, whereas when the setting ofthe governor spring 53A is that corresponding to idling conditions oroperation at low power, the fuel is delivered to the delivery passage 7throughout the whole of each delivery period at a reduced pressuredetermined by the pressure-reducing valve 39 and at a rate which is afunction jointly of the reduced pressure and the effectivecross-sectional area of the restrictor M. In this arrangement thereforethe injection characteristics under load-running conditions are similarto those in systems to which the invention is not applied but duringidling conditions a lower rate of injection by reason of the reducedpressure will be in operation.

in the modification shown in FIG, 5, which may be regarded as adiagrammatic illustration of an arrangement of pressurereducing valveassembly generally similar to that shown in FIG. 2, thepressure-reducing valve, here identified by the reference numeral M, issimilar to the pressure-reducing valve 237 in FIG. 2 except that,instead of the open passage 36 through which liquid pressure can be:applied directly to the piston member 31. in FIG. .2, thepressure-reducing valve 6d is provided with a passage 65 which opensinto a chamber M5 which is separated by a restricted passage as from achamber b7 in which liquid pressure acts on the piston member 32. Thesprings 6W and 7b shown diagrammatically in this construction correspondrespectively to the springs 29 and 33 in FIG. 2 while the passage 7llcommunicates with the inlet 6 of the injection device. The chambers asand 67 are formed in a restrictor plug titlA fixed in the bore of thevalve body.

in this construction, therefore, the operation is similar to that of theconstruction shown in FIG. 2 except that the rate of movement of thepiston device 32 during the initial part of each delivery period, beforeit uncovers the ports 22 and 25 to permit unrestricted flow of fuel fromthe passage 2 to the delivery passage 7, is a function of the reducedpressure determined by the pressure-reducing valve and at which fuelpasses into the chamber as and of the effective cross-sectional area ofthe restrictor 6ft. In effect therefore the arrangement may be regardedas similar to that shown in FIG. 2 but with the restriction 35 movedfrom the position shown in FIG. 2. into a position between thepressure-reducing valve 27 and the piston valve member 32.

What we claim as our invention and desire to secure by Letters Patentis:

l. A fuel injection system for internal combustion engines of theliquid-fuel-injection compression-ignition type, and comprising a fuelinjection device including a nozzle, a pressure chamber leading to thenozzle, and an injection valve controlling the flow of fuel from thepressure chamber to the nozzle, said injection system also comprisingfuel delivery means arranged to deliver fuel under supply pressure inpredetermined quantities at appropriately timed intervals to apressure-reducing valve having an outlet connected to the said pressurechamber, said pressure-reducing valve having an orifree of variablecross-sectiona1 area through which passes the flow of fuel delivered bysaid fuel delivery means, the crosssectional area of said orifice beingautomatically controlled by and in accordance with the'fluid pressuredownstream of said orifice to regulate said downstream fluid pressure toa constant reduced value substantially less than said supply pressureirrespective of variations in said supply pressure, said injection valvebeing opened automatically during each delivery period by the fuelpressure in said pressure chamber, and said pressure reducing valve whenoperative acting in each delivery period to reduce the fuel pressure atwhich fuel is delivered from the pressurereducing valve into saidpressure chamber to said constant reduced value and a restrictedmetering passage of fixed cross section arranged in series with thepressure-reducing valve and serving when the pressure-reducing valve isoperative to control the rate at which fuel is delivered to the pressurechamber at the said constant reduced pressure,

and means for rendering the pressure-reducing valve and the meteringpassage inoperative during periods when the delivery of fuel to thepressure chamber at substantially the full supply pressure is required.

2. A fuel injection system as claimed in claim 1 in which the said meansfor rendering the pressure reducing valve inoperative is arranged tomaintain the pressure reducing valve operative during a predeterminedinitial part of each delivery period and to bypass the pressure reducingvalve during the remainder of that delivery period.

3. A fuel injection system as claimed in claim 2, in which there isinterposed between the pressure reducing valve and the pressure chambera piston valve device which has a pressure face on which the outputpressure of the pressure reducing valve acts to move the piston valvedevice against a biassing force, and a working face serving during theinitial part of the said movement of the piston valve device to deliverfuel at the said constant reduced pressure to the pressure chamber andin which, after the said initial period of its movement, the furthermovement of piston valve device opens a passage which bypasses thepressure reducing valve to permit the flow of fuel to the pressurechamber at substantially the full supply pressure of the fuel deliverymeans.

4. A fuel injection system for internal combustion engines of theliquid-fuel-injection compression-ignition type, and comprising a fuelinjection device including a nozzle, a pressure chamber leading to thenozzle, and an injection valve controlling the flow of fuel from thepressure chamber to the nozzle, said injection system also comprisingfuel delivery means arranged to deliver fuel under supply pressure inpredetermined quantities at appropriately timed intervals to apressure-reducing valve having an outlet connected to the said pressurechamber, said injection valve being opened automatically during eachdelivery period by the fuel pressure in said pressure chamber, and saidpressure-reducing valve when operative acting in each delivery period toreduce the fuel pressure at which fuel is delivered from thepressure-reducing valve into said pressure chamber to a determinedconstant reduced value substantially below the full supply pressure ofthe fuel delivery means, and means for rendering the pressurereductionvalve inoperative during periods when the delivery of fuel to thepressure chamber at substantially the full supply pressure is required,said means for rendering the pressurereducing valve inoperative beingarranged to maintain the pressure-reducing valve operative during apredetermined initial part of each delivery period and to bypass thepressurereducing valve during the remainder of that delivery period,there being a piston valve device interposed between thepressure-reducing valve and the pressure chamber, said piston valvedevice having a pressure face on which the output pressure of thepressure-reducing valve acts to move the piston valve device against abiasing force, and a working face serving during the initial part of thesaid movement of the piston valve device to deliver fuel at the saidconstant reduced pressure to the pressure chamber, said piston valve,after the said initial period of its movement, being operable uponfurther movement to open a passage which bypasses the pressurereducingvalve to permit the flow of fuel to the pressure chamber atsubstantially the full supply pressure of the fuel delivery means, saidpressure-reducing valve also controlling a relief port on the pressureface side of the fuel delivery means, said pressure-reducing valve alsocontrolling a relief port on the pressure face side of the piston valvedevice, the pressurereducing valve being arranged to open the reliefport between fuel delivery periods to permit the return movement of thepiston valve device, and to close the relief port during its initialmovement at the start of each delivery period.

5. A fuel injection system as claimed in claim 4, including a restrictedpassage arranged in series with the pressure-reducing valve and servingwhen the pressure-reducing valve is operative to control the rate atwhich fuel is delivered to the pressure chamber at the said constantreduced pressure.

6. A fuel injection system as claimed in claim 5, in which therestricted passage is disposed between the working face of the pistonvalve device and the pressure chamber.

7. A fuel injection system as claimed in claim 5, in which therestricted passage is disposed between the pressure-reducing valve andthe pressure face of the piston valve device.

8. A fuel injection system for internal combustion engines of theliquid-fuel-injection compressiomignition type, and comprising a fuelinjection device including a nozzle, a pressure chamber leading to thenozzle, and in injection valve controlling the flow of fuel from thepressure chamber to the nozzle, said injection system also comprisingfuel delivery means arranged to deliver fuel under supply pressure inpredetermined quantities at appropriately timed intervals to apressure-reducing valve having an outlet connected to the said pressurechamber, said-injection valve being opened automatically during eachdelivery period by the fuel pressure in said pressure chamber, and saidpressure-reducing valve when operative acting in each delivery period toreduce the fuel pressure at which fuel is delivered from thepressure-reducing valve into said pressure chamber to a determinedconstant reduced value substantially below the full supply pressure ofthe fuel delivery means, and means for rendering the pressurereducingvalve inoperative during periodswhen the delivery of fuel to thepressure chamber at substantially the full supply pressure is required,said means for rendering the pressurereducing valve inoperative beingarranged to be operated by a control member serving to control directlyor indirectly the running of the engine to which the system is applied.

9. A fuel injection system as claimed in claim 8 in which the controlmember is arranged to control directly the quantity of fuel delivered bythe fuel delivery means during each delivery period.

10. A fuel injection system as claimed in claim 8 in which the controlmember controls the setting of a speed-responsive governor driven by theengine and actuating a fuel-metering control by which the quantity offuel delivered during each delivery period is varied.

11. A fuel injection system for internal combustion engines of theliquid-fuel-injection compression-ignition type, and comprising a fuelinjection device including a nozzle, a pressure chamber leading to thenozzle, and an injection valve controlling the flow of fuel from thepressure chamber to the nozzle, said injection system also comprisingfuel delivery means arranged to deliver fuel under supply pressure inpredetermined quantities at appropriately timed intervals to apressure-reducing valve having an outlet connected to the said pressurechamber, said injection valve being opened automatically during eachdelivery period by the fuel pressure in said pressure chamber, and saidpressure-reducing valve when operative acting in each delivery period toreduce the fuel pressure at which fuel is delivered from thepressure-reducing valve into said pressure chamber to a determinedconstant reduced value substantially below the full supply pressure ofthe fuel delivery means, and means for rendering the pressurereducingvalve inoperative during periods when the delivery of fuel to thepressure chamber at substantially the full supply pressure is required,said pressure-reducing valve comprising a valve housing containing amovable cylindrical valve shuttle which is rotatable in a surroundingcylindrical bore in the valve housing in addition to being axiallymovable therein, the shuttle when in a first orientation in the boremoving axially against an axial biasing force in response to variationsin the delivery pressure of the valve to regulate the said deliverypressure, but when turned into a second orientation in the boreproviding an unrestricted flow passage through which the full supply ofpressure of the fuel delivered means is transmitted through the valve tothe pressure chamber, and in which the means for bypassing or renderingthe valve inoperative comprises means for rotating the valve shuttleinto the second orientation.

12. A fuel injection system as claimed in claim 11 in which the valveshuttle is formed with a circumferential groove the said means forrendering the pressure-reducing valve inoperative is arranged to beoperated by a control member serving to control directly or indirectlythe running of an engine to which the system is applied, and in whichthe said control member is coupled to the valve shuttle by atransmission arranged to rotate the valve shuttle in response to controlmovements of the said control member.

1. A fuel injection system for internal combustion engines of the liquid-fuel-injection compression-ignition type, and comprising a fuel injection device including a nozzle, a pressure chamber leading to the nozzle, and an injection valve controlling the flow of fuel from the pressure chamber to the nozzle, said injection system also comprising fuel delivery means arranged to deliver fuel under supply pressure in predetermined quantities at appropriately timed intervals to a pressure-reducing valve having an outlet connected to the said pressure chamber, said pressurereducing valve having an orifice of variable cross-sectional area through which passes the flow of fuel delivered by said fuel delivery means, the cross-sectional area of said orifice being automatically controlled by and in accordance with the fluid pressure downstream of said orifice to regulate said downstream fluid pressure to a constant reduced value substantially less than said supply pressure irrespective of variations in said supply pressure, said injection valve being opened automatically during each delivery period by the fuel pressure in said pressure chamber, and said pressure reducing valve when operative acting in each delivery period to reduce the fuel pressure at which fuel is delivered from the pressure-reducing valve into said pressure chamber to said constant reduced value and a restricted metering passage of fixed cross section arranged in series with the pressure-reducing valve and serving when the pressure-reducing valve is operative to control the rate at which fuel is delivered to the pressure chamber at the said constant reduced pressure, and means for rendering the pressure-reducing valve and the metering passage inoperative during periods when the delivery of fuel to the pressuRe chamber at substantially the full supply pressure is required.
 2. A fuel injection system as claimed in claim 1 in which the said means for rendering the pressure reducing valve inoperative is arranged to maintain the pressure reducing valve operative during a predetermined initial part of each delivery period and to bypass the pressure reducing valve during the remainder of that delivery period.
 3. A fuel injection system as claimed in claim 2, in which there is interposed between the pressure reducing valve and the pressure chamber a piston valve device which has a pressure face on which the output pressure of the pressure reducing valve acts to move the piston valve device against a biassing force, and a working face serving during the initial part of the said movement of the piston valve device to deliver fuel at the said constant reduced pressure to the pressure chamber and in which, after the said initial period of its movement, the further movement of piston valve device opens a passage which bypasses the pressure reducing valve to permit the flow of fuel to the pressure chamber at substantially the full supply pressure of the fuel delivery means.
 4. A fuel injection system for internal combustion engines of the liquid-fuel-injection compression-ignition type, and comprising a fuel injection device including a nozzle, a pressure chamber leading to the nozzle, and an injection valve controlling the flow of fuel from the pressure chamber to the nozzle, said injection system also comprising fuel delivery means arranged to deliver fuel under supply pressure in predetermined quantities at appropriately timed intervals to a pressure-reducing valve having an outlet connected to the said pressure chamber, said injection valve being opened automatically during each delivery period by the fuel pressure in said pressure chamber, and said pressure-reducing valve when operative acting in each delivery period to reduce the fuel pressure at which fuel is delivered from the pressure-reducing valve into said pressure chamber to a determined constant reduced value substantially below the full supply pressure of the fuel delivery means, and means for rendering the pressure reducing valve inoperative during periods when the delivery of fuel to the pressure chamber at substantially the full supply pressure is required, said means for rendering the pressure-reducing valve inoperative being arranged to maintain the pressure-reducing valve operative during a predetermined initial part of each delivery period and to bypass the pressure-reducing valve during the remainder of that delivery period, there being a piston valve device interposed between the pressure-reducing valve and the pressure chamber, said piston valve device having a pressure face on which the output pressure of the pressure-reducing valve acts to move the piston valve device against a biasing force, and a working face serving during the initial part of the said movement of the piston valve device to deliver fuel at the said constant reduced pressure to the pressure chamber, said piston valve, after the said initial period of its movement, being operable upon further movement to open a passage which bypasses the pressure-reducing valve to permit the flow of fuel to the pressure chamber at substantially the full supply pressure of the fuel delivery means, said pressure-reducing valve also controlling a relief port on the pressure face side of the piston valve device, the pressure-reducing valve being arranged to open the relief port between fuel delivery periods to permit the return movement of the piston valve device, and to close the relief port during its initial movement at the start of each delivery period.
 5. A fuel injection system as claimed in claim 4, including a restricted passage arranged in series with the pressure-reducing valve and serving when the pressure-reducing valve is operative to control the rate at which fuel is delivered to the pressure chamber at the said constant reduced pressure.
 6. A fueL injection system as claimed in claim 5, in which the restricted passage is disposed between the working face of the piston valve device and the pressure chamber.
 7. A fuel injection system as claimed in claim 5, in which the restricted passage is disposed between the pressure-reducing valve and the pressure face of the piston valve device.
 8. A fuel injection system for internal combustion engines of the liquid-fuel-injection compression-ignition type, and comprising a fuel injection device including a nozzle, a pressure chamber leading to the nozzle, and in injection valve controlling the flow of fuel from the pressure chamber to the nozzle, said injection system also comprising fuel delivery means arranged to deliver fuel under supply pressure in predetermined quantities at appropriately timed intervals to a pressure-reducing valve having an outlet connected to the said pressure chamber, said injection valve being opened automatically during each delivery period by the fuel pressure in said pressure chamber, and said pressure-reducing valve when operative acting in each delivery period to reduce the fuel pressure at which fuel is delivered from the pressure-reducing valve into said pressure chamber to a determined constant reduced value substantially below the full supply pressure of the fuel delivery means, and means for rendering the pressure-reducing valve inoperative during periods when the delivery of fuel to the pressure chamber at substantially the full supply pressure is required, said means for rendering the pressure-reducing valve inoperative being arranged to be operated by a control member serving to control directly or indirectly the running of the engine to which the system is applied.
 9. A fuel injection system as claimed in claim 8 in which the control member is arranged to control directly the quantity of fuel delivered by the fuel delivery means during each delivery period.
 10. A fuel injection system as claimed in claim 8 in which the control member controls the setting of a speed-responsive governor driven by the engine and actuating a fuel-metering control by which the quantity of fuel delivered during each delivery period is varied.
 11. A fuel injection system for internal combustion engines of the liquid-fuel-injection compression-ignition type, and comprising a fuel injection device including a nozzle, a pressure chamber leading to the nozzle, and an injection valve controlling the flow of fuel from the pressure chamber to the nozzle, said injection system also comprising fuel delivery means arranged to deliver fuel under supply pressure in predetermined quantities at appropriately timed intervals to a pressure-reducing valve having an outlet connected to the said pressure chamber, said injection valve being opened automatically during each delivery period by the fuel pressure in said pressure chamber, and said pressure-reducing valve when operative acting in each delivery period to reduce the fuel pressure at which fuel is delivered from the pressure-reducing valve into said pressure chamber to a determined constant reduced value substantially below the full supply pressure of the fuel delivery means, and means for rendering the pressure-reducing valve inoperative during periods when the delivery of fuel to the pressure chamber at substantially the full supply pressure is required, said pressure-reducing valve comprising a valve housing containing a movable cylindrical valve shuttle which is rotatable in a surrounding cylindrical bore in the valve housing in addition to being axially movable therein, the shuttle when in a first orientation in the bore moving axially against an axial biasing force in response to variations in the delivery pressure of the valve to regulate the said delivery pressure, but when turned into a second orientation in the bore providing an unrestricted flow passage through which the full supply pressure of the fuel delivery means is transmitted through the valve to the pressure chamber, and in which the means for bypassiNg or rendering the valve inoperative comprises means for rotating the valve shuttle into the second orientation.
 12. A fuel injection system as claimed in claim 11 in which the valve shuttle is formed with a circumferential groove which cooperates with a pressure port in the side of the bore to provide the variable-area valve orifice for regulating the delivery pressure, and is formed in its cylindrical surface with one or more longitudinal grooves leading into the said circumferential groove, one or more of the longitudinal grooves being arranged to overlap the pressure port and provide the unrestricted flow passage when the shuttle is turned into its second orientation.
 13. A fuel injection system as claimed in claim 12 in which the said means for rendering the pressure-reducing valve inoperative is arranged to be operated by a control member serving to control directly or indirectly the running of an engine to which the system is applied, and in which the said control member is coupled to the valve shuttle by a transmission arranged to rotate the valve shuttle in response to control movements of the said control member. 